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Abstract:
Spasmodic Dysphonia (SD) is a voice disorder of unknown
etiology, characterized by a constellation of voice symptoms
resulting in bizarre speech. Structural and mucosal abnormalities
are absent and its diagnosis depends on perceptual evaluation.
Laryngoscopy and videofiberscopy, although commonly used for
evaluation of this disease, allow only the observation of gross
movements of anterior-to-posterior laryngeal squeezing and degree
of ventricular hyper function. The stroboscopic method, usually
used to evaluate vocal fold vibratory patterns, is not often used
due to the great variability in the frequency shifts that occur
during sustained phonation, thus making a precise evaluation of
the vocal fold vibration unfeasible. The application of the
advanced high-speed digital imaging system during sustained
phonation introduced a novel concept in the vocal fold vibratory
pattern in SD. With this technique, it was possible to verify
that there are three distinctive vocal fold vibration patterns
never described previously. The first pattern, where the closed
period of the vocal fold vibratory cycles are much longer than
the open period, has been assumed as the typical behavior of the
vocal folds in SD. The second pattern found was similar to that
previously described as a double vibratory patterning in vocal
fry phonation. The third and last pattern was a long closed
period followed by two open periods with a very short closed
period in between the open ones. The observation of the vocal
fold vibration showed that there is a great variability in
vibratory patterns during sustained phonation in spasmodic
dysphonia. These patterns, which were previously described as fry
phonation, may provide insights into the pathophysiology of this
disease. Further work is currently being conducted in SD patients
to verify if there are other vibratory patterns in SD and also
other work to search for possible causes of variability in the
vocal fold tension in order to better understand the etiology of
spasmodic dysphonia.
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